The Posi-drive screw

[Pete C]

For people who haven't yet discovered decent pozi bits :)

cheers, Pete.

[Dave Plowman (News)]

Phillips may have the patent on the cross head which the pozidriv needs a licence for - but at least pozidriv works well with the *correct* bit. As has been said, any parallel side hole like a square or torx doesn't work too well on a normal countersunk screw - it weakens it too much, or means it has to be larger.

[Bolted]

I'm not quite sure what you are saying there. They claim that they patented the pozidriv head after their patent protection on the phillips head expired, licensed it (pozidriv) internationally to GKN in 1966, and sold the lot, patents and all, to GKN in 1977.

There, that saved you *actually reading* the link.

As I said, they may be making it up. That seems unlikely, though.

[The Medway Handyman]

Depends on the make. IKEA use 4mm allen on their Confirmat screws, Wickes kitchen units use No3 pozi on Confirmats. Most flatpack includes normal woodscrews which are either pozi or phillips, but often a mixture of both.

[Andy Hall]

I've used dry wall ones in a Senco screw gun and they work better than Phillips. They may not be good in other applications.

[Bolted]

Fair enough. I've never done enough plasterboard (or decking, etc) to warrant getting a screwgun.

I bought a few packs of robertson drive screws because I was fed up of the cam out I was getting with a drill/driver on pozi (before I got my first impact driver, so that must be about 5 or 6 years ago). They just irritated me and were very slow to use - I found I had to make a conscious effort to get the bit lined up pretty precisely with the hole, start it slowly to get it to engage, then change to actually drive speed.

In comparison, I find Pozi a very clever balance between being self-locating for the bit and pretty good at resisting cam-out, so you can just point and press 'go', and onto the next.

[Dave Plowman (News)]

I'm afraid it doesn't *actually* say Phillips invented the Pozidriv. Talks about licensing it. It's rather vague. It does say GKN later acquired the sole rights for Pozidriv outside the US. It appears to be an in house history of the company and as much just flag waving as anything else.

[Andy Hall]

I think that that is fairly true. The Richardson ones are positive and work well if there isn't too much torque as long as one keeps an even pressure - screw gun tends to do that. I have used them separately from the bandolier and then they aren't as gooss as Pozidriv. OTOH, Torx is better than Pozidriv, I've found.

[The Medway Handyman]

I think Pozi definately win if you are installing lots of screws ala decking, especially with an impact driver. Pretty much self locating as you say.

Personally I think 'cam out' is caused by cheap screws, worn driver bits or insufficient pressure. Impact drivers are the way forward here. My new incy wincy Makita 7.2v jobby doesn't ever seem to cam out at all

I've been around the block with driver bits & have settled on el cheapo Wickes. You can buy 20 in a box for a couple of quid, they last fairly well, don't shatter and are cheap enough to change as needed. Thats the secret when installing say 2,200 screws on a deck - first suggestion of cam out - change the bit.

[Frank Erskine]

My new

I'm sure the 0·2v must make all the difference ;-)

Regards -

[Frank Erskine]

ITYM:- "c*ck waving"

[David in Normandy]

What is "cam out" - I'm not familiar with the term?

[Dave Plowman (News)]

I've just been using mine to lift and replace a load of floorboards all of which were screwed - and it's incredible. Initially I thought the fixed speed would be a problem but the clever slipping clutch overcomes this.

Good tip - I wondered where the best source was. Of course any worn screwdriver won't work properly and that applies to some new ones too - some makers simply don't make them to the correct spec for Pozidriv.

[Dave Plowman (News)]

I'd not dream of being so rude. ;-)

[David in Normandy]

- Is it when the bit starts to wear and spin in the screw slot?

[The Medway Handyman]

Oh yes! Useless without that extra bit.

Why do they make odd voltages like 7.2 & 14.4 anyway?

[Huge]

[Dave Plowman (News)]

It's where the bit gets pushed up out of the screw due to wear or being off square. Rather than just stripping or snapping as would happen with a parallel sided hole like a square or torx etc. You'll feel the drill bounce up and down rather like a valve in a car - hence cam as in camshaft.

[Mike Barnes]

It's chemistry. They can't make any voltage they feel like.

[Dave Plowman (News)]

The cells used are nominally 1.2v each. So the common voltages of drills sort of revolve around how easy it is to package the cells in the battery, rather than 14.2 etc being the exact ideal voltage for the tool.